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| Bandwidth check of my oscilloscope with simple means ? |
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| David Hess:
--- Quote from: tggzzz on December 11, 2020, 08:24:03 pm --- --- Quote from: Berni on December 11, 2020, 08:13:23 pm ---One thing to keep in mind when testing probes like this is that at high frequency the >10pF of probe capacitance starts to really matter and can drag down a 50 Ohm source, but up to 100MHz it's still pretty reasonable. --- End quote --- 15pF at 100MHz is ~100ohms. So much for such a probe being "high impedance 10Mohm"! --- End quote --- Indeed, probe bandwidth is specified with a 25 ohm source impedance and a coaxial connection to the probe tip, which is unrealistic for most real world usage up to 100 or even 200 MHz because of the inconvenience. |
| rifkum:
I know this is a very old thread... but this is an interesting topic and new scope owners may be interested in the topic subject... Alan is a very good teacher and here is his video on measuring scope bandwidth. https://youtu.be/Ly5pmYopEfU?si=f5Q5FRmHvXZYNN_P Cheers |
| vk6zgo:
--- Quote from: tggzzz on December 10, 2020, 08:18:33 pm ---Of course you can never measure a waveform with a scope, only with a scope plus probes. There are many pitfalls for the unwary associated with poor probing technique. --- End quote --- So all those times I looked at signals coming out of the 50 Ohm or 75 ohm output of a DUT, (with the correct termination on the 'scope), I was doing it wrong? ;D Thread too old for my "smart comment" & besides, tggzzz has already addressed this point in a later posting. :-[ |
| David Hess:
--- Quote from: vk6zgo on February 10, 2024, 04:22:25 am --- --- Quote from: tggzzz on December 10, 2020, 08:18:33 pm ---Of course you can never measure a waveform with a scope, only with a scope plus probes. There are many pitfalls for the unwary associated with poor probing technique. --- End quote --- So all those times I looked at signals coming out of the 50 Ohm or 75 ohm output of a DUT, (with the correct termination on the 'scope), I was doing it wrong? ;D Thread too old for my "smart comment" & besides, tggzzz has already addressed this point in a later posting. :-[ --- End quote --- If I had noticed it, then I would have addressed it. I measure waveforms using an oscilloscope without a probe all of the time. Indeed, I have never used a probe on my sampling oscilloscope. Closer to the context of tggzzz's statement, many of my oscilloscopes return identical results when measuring the bandwidth of the instrument with and without a probe, but this will not be the case with all oscilloscopes. |
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